1. Field of the Invention
This invention relates to an elbow prosthesis, and more particularly to a replacement for the radial head and to methods and instruments for use in replacing a radial head.
2. Description of the Related Art
Fractures of the radial head constitute one of the most common fractures of the elbow. Radial head fractures can be treated by excision of the head of the radius. However, this can lead to joint pain and elbow instability. As a result, prosthetic radial head replacements have been frequently recommended to obviate the problems associated with excision of the radial head and to improve stability of the elbow joint. Examples of a radial head prosthesis are shown in U.S. Patent Application Publication Nos. 2003/0212457 and 2001/0037154, and in U.S. Pat. Nos. 6,656,225, 6,361,563, 6,270,529 and 6,217,616.
Radial head replacements generally include a stem portion designed to extend into the intramedullary canal of the radius and a head portion designed to replace the radial head. When replacing the radial head with a radial head replacement, the radial head is surgically removed and the top of the radius and the intramedullary canal of the radius are prepared for receipt of the stem. A cement material is typically inserted into the open intramedullary canal and the stem is driven into the canal. Often, the stem is fixed to the radius with a curable acrylic polymer cement such as polymethylmethacrylate. Alternatively, the stem may be fixed to the radius using an interference fit (i.e., “press fit”) without cement. In another alternative, the radial head replacement may be fixed to the radius using bone screws.
While existing radial head replacements provide satisfactory results for most purposes, they do have drawbacks. For example, it may be difficult to position known radial head replacements such that the end surface of the head portion of the implanted radial head replacement smoothly interfaces with the capitellum of the humerus. In extreme cases, the implanted radial head replacement may even dislocate such that intefacial contact with the capitellum is precluded.
One source of this positioning problem is the lack of adjustability of known radial head replacements. Existing radial head replacements are typically unitary in design and therefore, do not allow for relative movement between the stem portion and the head portion. Thus, the position of the head portion cannot be adjusted in relation to the stem portion after the stem portion is inserted in the intramedullary canal of the radius.
Another source of this positioning problem is the inaccuracy of some osteotomy cuts of the natural radial head. Generally, the osteotomy cut of the natural radial head must be made so that the angle of the cut corresponds to the angle between the stem and head portions of the radial head replacement. Inaccurate resection can result in an ill-fitting radial head replacement which may lead to the dislocation risks noted above. Various resection guides have been proposed in the orthopedic field. See, for example, U.S. Pat. Nos. 5,779,709, 5,704,941, 5,601,565, 5,108,396, 4,927,422, 4,736,737, 4,718,414, and 4,686,978 and U.S. Patent Application Publication Nos. 2003/0158558 and 2003/0114859.
Another problem with radial head replacement procedures may develop from the employment of a bone cement for fixation of the stem to the radius. This problem is primarily related to limitation of the cement to the area of the stem within the intramedullary canal of the radius. Specifically, the cement may travel beyond the area of affixation in the radius. Proper fixation of the stem to the radius may not be achieved without taking steps to limit the travel of the cement. U.S. Pat. No. 4,302,855 has proposed one solution to this problem.
Yet another problem with radial head replacement procedures may develop from the use of bone screws for fixation of the radial head replacement to the radius. For example, bone screws may not provide for optimum fixation of the radial head replacement to the radius.
Thus, there is a need for an improved radial head replacement that provides for better contact with the capitellum of the humerus. In particular, there is a need for a radial head replacement that can be adjusted so that the head portion of the implanted radial head replacement smoothly interfaces with the capitellum of the humerus. There is also a need for a radial head replacement that provides for improved fixation of the radial head replacement to the radius. There is also a particular need for a radial cutting guide which ensures a precise resection of the radial head and thereby allows for better positioning of the implanted radial head replacement. There is also a need for a means for limiting the travel of bone cement beyond the area of affixation of the stem portion of a radial head replacement to the radius.